Not applicable.
Not Applicable.
The preferred embodiments of the present invention generally relate to dual energy exposure techniques, and in particular relate to using image information to control dual energy exposure techniques.
X-ray imaging has long been an accepted medical diagnostic tool. X-ray imaging systems are commonly used to capture, as examples, thoracic, cervical, spinal, cranial, and abdominal images that often include information necessary for a doctor to make an accurate diagnosis. X-ray imaging systems typically include an x-ray source and an x-ray sensor. When having a thoracic x-ray image taken, for example, a patient stands with his or her chest against the x-ray sensor as an x-ray technologist positions the x-ray sensor and the x-ray source at an appropriate height. X-rays produced by the source travel through the patient""s chest, and the x-ray sensor then detects the x-ray energy generated by the source and attenuated to various degrees by different parts of the body. An associated control system obtains the detected x-ray energy from the x-ray sensor and prepares a corresponding diagnostic image on a display.
The x-ray sensor may be a conventional screen/film configuration, in which the screen converts the x-rays to light that exposes the film. The x-ray sensor may also be a solid state digital image detector. Digital detectors afford a significantly greater dynamic range than conventional screen/film configurations.
One embodiment of a solid state digital x-ray detector may be comprised of a panel of semiconductor Field Effect Transistors (FETs) and photodiodes. The FETs and photodiodes in the panel are typically arranged in rows (scan lines) and columns (data lines). A FET controller controls the order in which the FETs are turned on and off. The FETs are typically turned on, or activated, in rows. When the FETs are turned on, charge to establish the FET channel is drawn into the FET from both the source and the drain of the transistor. The source of each FET is connected to a photodiode. The drain of each FET is connected to readout electronics via data lines. Each photodiode integrates the light signal and discharges energy in proportion to the x-rays absorbed by the detector. The gates of the FETs are connected to the FET controller. The FET controller allows energy discharged from the panel of photodiodes to be read in an orderly fashion. The readout electronics convert the energy discharged from photodiodes to electrical signals. The energy discharged by the photodiodes in the detector and converted by the readout electronics is used by an acquisition system to activate pixels in the displayed digital diagnostic image. The panel of FETs and photodiodes is typically scanned by row. The corresponding pixels in the digital diagnostic image are typically activated in columns.
The FETs in the x-ray detector act as switches to control the charging of the photodiodes. When a FET is open, an associated photodiode is isolated from the readout electronics and is discharged during an x-ray exposure. When the FET is closed, the photodiode is recharged to an initial charge by the readout electronics. Light is emitted by a scintillator in response to x-rays absorbed from the source. The photodiodes sense the emitted light and are partially discharged. Thus, while the FETs are open, the charge on the photodiodes moves to a charge level representative of the x-ray dose. When a FET is closed, a desired voltage across the photodiode is restored. The measured charge amount to re-establish the desired voltage becomes a measure of the x-ray dose integrated by the photodiode during the length of the x-ray exposure.
X-ray images may be used for many purposes. For instance, internal defects in a target object may be detected. Additionally, changes in internal structure or alignment may be determined. Furthermore, the image may show the presence or absence of objects in the target. The information gained from x-ray imaging has applications in many fields, including medicine and manufacturing.
A common type of cancer today in the United States is lung cancer. Lung cancer is fatal at an extremely high percentage of the time when not detected early enough. However, no good screening process is known to exist. One proposal is to use CT (computed tomography) systems to screen for lung cancer. However, the cost and dosage for a screening application may be prohibitive.
xe2x80x9cRADxe2x80x9d is a term that denotes single shot radiography. For example, a typical chest film taken at a hospital is taken with a RAD system. X-rays for broken bones are also often taken with RAD systems. Digital RAD systems are typically cheaper and use less dosage for an examination than CT systems. Additionally, the staging requirements (especially floor space) are less as well, simplifying the concept of a dedicated screening room.
However, conventional RAD systems do not have the discrimination needed to see lung cancer nodules at an early stage of development even though RAD systems produce high resolution images. The lung cancer nodules are high contrast (compared to air), and, thus, a dominant issue for RAD systems is fixed pattern background noise (i.e., the ribs) present in an x-ray image. A technique called dual energy can separate the soft tissues from the bones creating 2 output images. The soft tissue image has the structured background noise removed. Dual energy allows one to view the cancer nodules without the ribs, allowing the nodules to stand out clearly against the soft tissue.
An alternative imaging technique to dual energy exposure is a CR (computed radiography) system. A CR system has a detector with two detector areas. In a CR system, a first detector is located behind a second detector. In a CR type system, only one exposure is taken by the two detectors. Since only one exposure is taken, a CR type system may reduce the energy exposure dosage that a patient receives. One drawback of a CR system is that the second detector exhibits very high noise. The second detector also only allows a low exposure. As a result, the difference in energies between the two detector images is limited. In other words, there is very low discrimination between the detector images. In order to get a sufficiently high separation in exposure energies and a sufficiently high signal-to-noise ratio (SNR) for the second (high x-ray energy) image, the patient dose would be excessive.
Conventional RAD systems have been proposed that operate based on the concept of dual energy, in accordance with which a system that takes two exposures, one low energy and one high energy, to separate the soft tissue (a low energy absorber) from the bone (a high energy absorber). The second exposure deposits extra dose to the patient, and therefore it is desirable to adjust the second exposure dependent on the patient characteristics. In addition image quality can be optimized by regulating the proportion of dose between the 2 exposures.
A need remains for a system that uses anatomical information in an image to control and adjust the parameters for the second exposure.
A preferred embodiment of the present invention provides a method and apparatus for dual energy image acquisition. The method comprises obtaining an image from a first exposure of a patient and segmenting the image into an anatomy of interest. The method further comprises characterizing the segmented anatomy in terms of a set of patient parameters and adjusting exposure characteristics for a second exposure of the segmented anatomy based upon the set of patient parameters and the characterization of the anatomy. The resulting anatomic images are obtained from analysis of the first and second exposures. In an alternative embodiment, said first exposure may be a low dose scout exposure. Then the 2nd and 3rd exposure would be optimize and used for the subsequent dual energy decomposition. In a preferred embodiment, the set of patient parameters may include attenuation of the segmented anatomy, normalized patent data, and a mathematical model of the segmented anatomy.
A preferred embodiment of the system comprises a dual energy medical imaging system, a detector, a user interface, an image segmentation module, a characterization module, and a control module. The dual energy medical imaging system is adjustable for various exposure dosage levels and techniques. In an alternative embodiment, the dual energy medical imaging system may be adjusted for a low dose scout exposure. In a preferred embodiment, the dual energy medical imaging system adjusts between a first exposure dosage level and a second exposure dosage level. The detector converts exposure energy into digital signals. In a preferred embodiment, the exposure energy comprises x-ray energy. The interface allows a user to set image acquisition parameters. The image segmentation module identifies an anatomy of interest. The characterization module characterizes the anatomy of interest according to a set of patient parameters. The control module optimizes the subsequent dual energy image acquisition. In a preferred embodiment, the system further comprises an output for displaying the resulting anatomy images.